The present invention relates to a substrate of an electronic circuit and more particularly to a circuit substrate composed of a resin and to a method therefor.
A conventional substrate of an electronic circuit comprises a wiring substrate and electronic parts. The wiring substrate includes a base substrate and a metal foil such as copper foil laminated on the base substrate. The electronic parts are mounted on the base substrate. The base substrate is made of a compound resin consisting of a mixture of glass and epoxy resin or, a mixture of paper and epoxy resin, or a mixture of paper and phenolic resin, a mixture of glass and polyimide resin. The copper foil is etched to form a pattern thereon to manufacture the wiring substrate. Electronic parts are arranged on the wiring substrate to solder the electrodes thereof into those of the wiring substrate so that the electronic parts are fixed to the wiring substrate and electrically connected thereto. Thus, an electronic circuit substrate is constructed.
However, the above-described prior art has the following problems:
First, the material for connecting the electrodes of the electronic parts to those of the wiring substrate is required to perform the function of retaining the electronic parts therein and accomplishing an electrical connection. That is, the material is required to have both the characteristics of a preferable adhesive strength and a connection resistance value. It is known that Sn/Pb alloy is the most reliable material for bearing the above two characteristics. As such, in the manufacture of an electronic circuit substrate, conventionally, soldering is necessarily employed to connect the electronic parts to the wiring substrate. It is expensive to provide a factory with equipment for performing a soldering operation, disposing a washing solution and a discharged gas, and preventing environmental pollution. Therefore, there are growing demands not only for the development of a technique, which replaces soldering, for connecting the electrodes of the electronic parts to those of the wiring substrate, but also for the development of a technique for manufacturing a circuit substrate.
Secondarily many steps are required to manufacture the conventional resin wiring substrate, including: adhesion of the base substrate to a prepreg plate; lamination of a copper foil on the base substrate; hardening of a resin; resist application to the wiring portion; photo-etching; wet copper foil etching; cleaning of the portion to be soldered; soldering operation; and application of resist and hardening thereof. In order to perform these operation steps, expensive equipment must be provided and delicate workmanship is required to manufacture a precise circuit substrate.
Thirdly, compared with a purchase price of a resin wiring substrate, a user is required to pay more to manufacture the resin wiring substrate by himself in order to shorten the lead time and manufacture it with desired electron parts depending on the production conditions.
Fourthly, in the conventional resin circuit substrate, fine electronic parts which have come into increasingly frequent use in recent years are not mounted on the wiring substrate with high accuracy. That is, in order to mount fine electronic parts on the wiring substrate with high accuracy of within 0.05 to 0.1, it is necessary to take the following measures: The utilization of the adhesiveness of a creamed material for use in a soldering or an adhesive agent exclusively used for electronic parts; the use of a device for reducing the vibration of an electronic parts mounting equipment; and the improvement of a nozzle structure used to mount electronic parts on the wiring substrate. However, accurate electronic circuit substrates are manufactured at a low percentage because electronic parts are not mounted on the wiring substrate at high accuracy.